Today mobile terminals often poll multiple services by sending packets to these services and expecting an answer. Does this terminal have e-mail waiting? Are there incoming instant messaging (IM) messages? Is there an update to a web page that the device is interested in?
This consumes a lot of resources from the network, and has been the cause of major network capacity problems, e.g., as smartphones were introduced. Moreover, having to frequently send and receive data to and from the network requires the terminal to be in active state most of the time which increases the energy consumption and results in short standby time.
There are only limited mechanisms for the network to inform the terminal that it has some traffic. One of these mechanisms is that the network provides ability to page a device that has some incoming IP packets. Paging is essentially carried out by transmitting the identifiers of the terminals to be paged over a specific paging channel. As an example, Long Term Evolution (LTE) networks employ the following techniques (see 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 36.331):                The paging channel is divided into time-based paging occasions and a numeric algorithm based on the identities of the terminals is used to determine at which occasion a particular terminal shall be paged at (i.e., the paging group). The terminal needs to monitor the paging only during its paging slot. This limits the amount of listening a terminal needs to do, thus improving battery lifetime.        If a terminal should be paged, in the occasion for this terminal, the system transmits its S-Temporary Mobile Subscriber Identity (S-TMSI, temporary, unique identifier) or sometimes IMSI (International Mobile Subscriber Identity). If multiple terminals need to be paged in the same slot, their S-TMSI (or IMSI) values are listed (up to the length of the slot, maximum of 16 terminals in LTE 3GPP Release 10).        
In general, existing paging mechanisms can be divided into the following groups:    1. Agreeing on a specific time slot or channel where devices should listen for incoming messages for them.    2. Multi-stage mechanisms where the devices are not given a message directly, but only an indication that a message is coming and possibly some further information at which time, on which channel, etc. either the message or some further instructions can be received.    3. Designating specific devices to listen for a message at a specific time slot or channel.    4. Identifying specific devices in a message by their identifiers.    5. Identifying groups of devices in a message by some partial identifier, e.g., the first N bits of an M bit identifier (M>N).    6. Identifying groups of devices with some dynamic identifier that has to be agreed between the network and the devices.    7. Using a Bloom filter or some other construct to create a space-efficient bit pattern that identifies which nodes need to woken up.
Nevertheless, the paging mechanism is only applicable when there is a peer that has sent a packet to the terminal.
Another related mechanism includes the use of a common transport channel and an intermediate server, to consolidate polling of different services. This is used by certain modern smartphone platforms. The idea is that the phone communicates over one Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) session with a server in the phone manufacturer's network, and that server then contacts the necessary other services. This reduces the amount of packets needed to be sent from the mobile terminal.